Health monitoring of an emblematic monument by terrestrial laser scanning: Fid-Bau Portal

Health monitoring of an emblematic monument by terrestrial laser scanning

Munoz-Nieto, A. / Gonzalez-Aguilera, D. / Gomez-Lahoz, J. / Herrero-Pascual, J.

The first measurement took place in May 2007. Its main goal was to provide a base line, ie a description of the structure's initial state (with zero deformation), as well as confirming a possible collapse of the structure. With this in mind, a full and detailed metric digital recording was obtained based on a TLS Trimble GX 200. This first measurement was instrumental in establishing the reference coordinate system using control points located over stable elements outside the main wall. After processing the range data set corresponding to the first measurement, two main structural problems were diagnosed. The first and most important problem was an out of plumb of 12 cm (Figure 2), located in the upper part of the structure. The second was a convex deformation of 9 cm in the outer part of the wall, located in the lower part of the structure. After six months (October 2007), a second measurement was taken to check for possible deformation of the structure. It was vital that an accurate and reliable deformation measurement was provided, in order to analyse structural behaviour. Structural monitoring was established between both measurements based on multiple orthogonal cross sections applied to the 3-D surfaces (Figure 3). From the analysis of Figure 3, the following were asserted: a uniform collapse of 3 cm towards the outer part of the wall and the out of plumb of the upper part of the structure had increased by up to 15 cm. This confirmed the collapse of the structure. In November, after the two measurements had been taken and the results obtained, the Local Authority designed an emergency plan to secure and maintain the safety and serviceability of this significant monument. A special metal structure was built to stabilise the wall and prevent further collapse (Figure 4). A third measurement was taken in December 2007 to ensure the structure's stability and check for anything unusual that could be linked to the metal structure. The results have only served to confirm its stability. To conclude, it is hoped that the storks will be able to use their summer residence next year and tourists can enjoy seeing them!